There are many reasons a person might wish to wear a face mask that filters particulates from the air that is breathed. In an area having high air pollution this is desirable, simply to protect the respiratory and cardiovascular systems of the face mask wearer. Further there are many work situations, for example concrete sawing, or removing old paint with a sander, where encountering air filled with particulates is inevitable. With the familiar disposable face mask, the wearer must draw in air sufficiently to go through the face mask. For the young and the elderly, this may be difficult. Additionally, familiar disposable face masks often suffer from a lack of air ventilation, which can cause discomfort as excessive heat and moisture to build up.
There are many difficult trade-offs in the design of a particulate filter face mask. The smallest particles, those below 25 micrometers in size, pose the greatest threat to human health, as they may enter the smallest portion of the alveoli and may even enter the blood stream. Yet a filter that can filter out such tiny particle will offer a greater resistance to air flow, potentially making breathing difficult, and will tend to clog up faster, requiring more frequent changes of filter material.
Even for face masks equipped with motorized air-supply systems, the fan and power supply units are often too bulky and heavy to be comfortable and mobile. Although a number of face masks have been proposed having integrated portable fan assist in order to achieve comfort, mobility and higher filtration efficiency, none of them appear to have met with great commercial success. One issue is the difficulty of having a fan push all of the required air through a filter. A normal adult draws an in-breath about 12 times per minute. Each inhale takes about 0.5 litter (0.018 cubic feet) of air, which translates to a total of about 6 liters per minute (0.21 cubic foot per minute [CFM]). On average, a human can breathe 12 to 35 times per minutes and take in average 0.5 liter to 6 liter air per inhale resulting in a rate of 0.5 CFM to 6 CFM. This drives a requirement for a large, heavy fan that tends to weigh down a wearer, and may even create a rather loud sound that may be unwelcome to the user.
Unfortunately, wearing currently available masks can be uncomfortable or ineffective. The simple, commonly available disposable masks tend to leave a space between the mask boundary and the face, thereby potentially permitting particulates to enter the mask wearer's airways. Forming a seal between the mask and the wearer's face, however, risks a loss of comfort. The great variety of facial shapes makes a particular challenge of finding a mask structure that adequately serve the broad range of the public.
Another issue with having a currently available mask with a fan is that fan replacement, either in the event of a broken fan, or to exchange a current fan for one with different characteristics, can be quite difficult. Also, the currently available design in which a filter fits about an air valve risks cross contamination when the filter is exchanged. Further, fans permanently set into a face mask according to currently available designs also risk cross-contamination and are a challenge to clean and sterilize.